Texture Directionality

Texture or structure in an image may also have directionality. This can be detected as a property and used to label regions by applying the same Sobel brightness gradient vector introduced above as an edge delineation tool. The magnitude of the vector was used to outline steps and edges. The orientation angle of the vector can be used to characterize local orientation. The angle from 0 to 180 or from 0 to 360 degrees is generally scaled to the 0..255 brightness range of the display, or shown as a color. For the directions and cloth images this shows that the visually distinct regions of the image can be separated by the procedure. For the collagen image, the histogram is a quantitative measure of the preferred orientation of the fibers. This interactive Java tutorial illustrates the use of the angle of the local brightness gradient vector to convert textural orientation differences to brightness differences for regions in an image.

The tutorial initializes with a randomly selected specimen appearing in the Specimen Image window. The Choose A Specimen pull-down menu provides a selection of specimen images, in addition to the initial randomly chosen one. The histogram of the brightness values in the image is shown in the right-hand Histogram window. Clicking on the Grayscale Orientation button shows the processed result for the image and histogram, illustrating the introduction of brightness differences that can be thresholded to select the various regions. Clicking on the Color Orientation button substitutes colors for the grayscale values in the processed image.